The primary objective of this application is to conduct the initial clinical testing of new bispecific antibody (bsMAb) pretargeting system that uses a 90Y-labeled peptide for the treatment colorectal cancer. Our hypothesis is that this pretargeting study will be able to increase the radiation dose delivered to the tumor in comparison to what has historically been achieved with directly radiolabeled antibodies. The bispecific antibody used in this clinical trial is a novel humanized recombinant bsMAb with divalent binding to carcinoembryonic antigen (CEA) for tumor targeting and monovalent binding to a unique compound, histamine-succinyl-glycine (HSG). The peptide has 2 HSG molecules that aid in the stabilization of the bsMAb when bound to the tumor cell surface and a single DOTA moiety suitable for binding 111In and 90Y. The clinical trial will seek to find the optimal conditions for pretargeting the 111In/90Y-labeled peptide using the novel bispecific triabody (81 kDa). These initial studies will examine several doses of the bsMAb and peptide with the peptide given at differing time intervals after the bsMAb injection. 131I-bsMAb is planned to be given to aid in determining the localization properties of the bsMAb, and each patient will receive a combination of the 111In- and 90Y-labeled peptide. In the initial testing, the 90Y-dose of peptide will be fixed so that the parameters of pretargeting can be determined. In the Phase I portion of the trial, optimum conditions to allow maximum tumor accretion of the peptide with minimal normal tissue accretion will be used, but the 90Y-radioactivity dose will be escalated to determine the dose limiting toxicity and the MTD. Quantitative imaging and pharmacokinetics will be examined in all patients over several days following the radiolabeled peptide injection to aid in the assessment of conditions that will yield the highest accretion of radiolabeled peptide in the tumor, while minimizing normal tissue accretion. Anti-antibody responses will also be measured to the humanized bsMAb. This clinical trial will be conducted at the Fox Chase Cancer Center. [unreadable] [unreadable]